I have a couple cornies of the old Firestone variety that have abrasions all over the top surface of the liquid-out posts. Will this cause a sanitation problem since they'll be in a cold fridge anyway (which should retard bacterial growth) or should I just replace them?

If you wanted to be sure, take the poppets out and boil the hell out of the post. The heat will kill anything hiding in the gouges. I'd only do that every few batches and just dip in your sanitizer for the other batches.

Some of the old firestone parts like pop off valves are no longer being made as near as I can tell. From what I've seen the parts for some of these old kegs cost almost as much or more that what you'd spend on another used keg that does not have any problems. Check out parts $ then the price of used kegs as low as $15 for a single handle keg and see what makes the most sense to you.

These kegs do hold pressure. I've already cleaned and reconditioned them with O-rings and poppets, and replaced lids on three of them with used Cornelius ones since replacement pressure relief valves on the old Firestone lids were impossible to find. The kegs were $18 but were really nasty when I got them.

New liquid posts for these kegs are about $8 each I think. Not much really, but almost half of what I paid for the whole keg before replacing other parts.

I think I'll try the "boil the hell out of it" suggestion and hope for the best.